Foil for dry shavers



May 12, 1970 N. T. SANDERS FOIL FOR DRY SHAVERS 2 Sheets-Sheet 1 Filed Nov. '7, 1967 y 1970 N. T. SANDERS 3,510,942

FOIL FOR DRY SHAVERS Filed Nov. 7, 1967 2 Sheets-Sheet 2 IMVMT R'.

NORMAN THOMAS sauna Rs N J \LJMM United States Patent 3,510,942 FOIL FOR DRY SHAVERS Norman Thomas Sanders, Studley, England, assignor to Wilkinson Sword Limited, London, England, a British company Filed Nov. 7, 1967, Ser. No. 681,249 Int. Cl. B26b 19/42 US. Cl. 30-342 ABSTRACT OF THE DISCLOSURE A guard member (sometimes known as a shear plate) to cooperate with the cutt r member of a dry shaver is formed in a conventional manner from carbon or stainless steel between 0.0015 and 0.005 inch in thickness with apertures, which need not be circular, 0.015 to 0.025 inch across and at least approximately 0.006 inch apart. The surface of the foil which is in contact with the cutter member is formed with a recessed pattern of straight or curved grooves or of discrete indentations between 0.0001 and 0.0002 inch in depth and typically 0.003 inch wide and 0.001 inch apart so that the boundary of such an aperture intersects the recessed pattern and is thus of castellated, wavy, or other undulating form in the direction of the thickness of the foil.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to metal foils of the type used in the construction of dry shaver cutting heads. In dry shavers the cutting head comprises a cutter member which either is reciprocated linearly or angularly, or is rotated by an actuating mechanism, and is usually formed as one or more blade elements mounted on a carrier member. The blade elements move in sliding engagement the lower surface (hereinafter called the running surface) of an apertured foil member herein called the guard member (but sometimes known as the shear plate) to cut hair projecting through the apertures when the outer surface of the guard member engages the users skin.

Description of the prior art Metal foils for guard members of dry shavers have usually been formed with both the running surface and the other surface which in use contacts the users skin, of plain form. According to one prior proposal the running surface may be recessed in such a manner that the apertures, which are noncircular, are surrounded by a wall or rim. Such wall or rim however extends totally around the periphery of the aperture so that the boundary thereof runs in a single plane which defines the effective running surface of the foil.

It is an object of the invention to provide a foil Which will produce a closer shave without loss of gathering power and hence improve the efliciency of a dry shaver employing such a foil.

SUMMARY OF THE INVENTION According to one aspect of the invention we provide a foil, for a dry shaver guard member, formed with a plurality of apertures extending therethrough having dimensions in the plane of the foil substantially greater than the thickness of the foil, the running surface of the foil being formed with a recessed pattern having a configuration such that the boundary of each such aperture meets said running surface in an undulating line.

The term undulating is to be deemed to include both discontinuous variations so that the line is of stepped or castellated form and continuous variations so that the line is of sinuous or wavy form.

8 Claims "ice.

Said recesses may comprise a plurality of channels, which term is herein used to include laterally adjacent parts of a single complex groove or of a plurality of grooves which are joined by connecting portions, as well as a plurality of separate grooves. Thus the channels may be formed as a continuous spiral groove, or as several continuous grooves comprising a multistart spiral, or as an array of straight parallel grooves, or concentric circular grooves.

Alternatively, the pattern may comprise a plurality of discrete indentations, and preferably the size and distribution of such indentations are such that the boundary of each such aperture intersects a plurality of such indentations.

In making a foil of the invention, the foil is first treated to form the recesses in the running surface and is subsequently treated to form the apertures.

The recesses may be formed by rolling or stamping so as to deform the foil, and the apertures may be formed by piercing the foil.

Preferably, however, both the recesses and the apertures are formed by etching, in which case the apertures can readily be of noncircular shape.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described by way of example with reference to the accompanying drawings wherein:

FIG. 1 shows a fragmentary underneath plan view of a dry shaver guard member made from foil in accord ance with the invention,

FIG. 2 shows a detail from FIG. 1 on enlarged scale,

FIG. 3 shows a cross section on the line IIIIII of FIG. 2, on a still greater scale and also shows a portion of the associated cutter member,

FIG. 4a: shows diagrammatically a recessed pattern in the foil of FIG. 1, the width and spacing of the recesses not being shown to scale,

FIGS. 4b, 4c, 4d show respective modifications of the pattern of FIG. 4a, and

FIG. 5 shows a detail similar to FIG. 2 of an alternative type of foil.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A typical foil in accordance with the invention may be formed from carbon or stainless steel of thickness in the range 0.0015 to 0.005 inch, a preferred thickness being 0.002 inch.

The foil 10 illustrated in FIGS. 1 to 3, and 4d is formed as an inner part of a guard member, for a shaver having a rotating cutter member 10a, as described in my Pat. No. 3,197,864 and to which reference may be had for a full description thereof. On its running surface 11 which is contacted by the cutter member 10a the foil 10 is formed with a plurality of recessed portions forming a recessed pattern comprising a plurality of cannels which are formed as concentric grooves 12 of squared shape in transverse cross section. These grooves 12 are typically between 0.0001 and 0.0002 inch deep, the preferred value being 0.00015 inch. The grooves 12 are typically 0.003 inch wide and separated by lands 13 typically 0.001 inch wide which constitute the contact portion of the running surface. The other surface of the foil is plain. The foil is perforated by apertures 14 of circular shape which have a diameter in the range 0.015 to 0.025 inch, typically 0.020 inch. Each aperture 14 is separated from its nearest neighbouring aperture by bridge portions 15 of minimum width of about 0.006 inch.

Thus each aperture 14 intersects five or six grooves 12 and six or five lands 13. In this way the orifices of the apertures 14 at the running surface 11 of the foil when viewed in the plane of the foil (as seen in FIG. 3) are of toothed or castellated form. The lengths of the portions 1611-1 (FIG. '2) of the orifice of each aperture which are formed by the bottoms of the grooves 12 will vary according to the disposition of the grooves relatively to the aperture as can be clearly seen in FIG. 3. Similarly, the length of the portions 16k-t of the orifice which are formed by the surfaces of the lands between the grooves will also vary. Thus generally each aperture intersects two lands (13c and 13d, FIG. 2) which at the point of intersection are at least approximately radially arranged and two lands (13a and 13 which are approximately tangentially arranged at the point of intersection, the remaining lands (13b and 13e) being intersected at an intermediate angle.

'Instead of a plurality of concentric grooves 12 the channels may comprise adjacent convolutions of a continuous spiral groove as shown diagramatically at 12a in FIG. 417. A plurality of concentric spiral grooves forming a multistart spiral could also be employed as shown diagrammatically at 12b in FIG. 4c with the advantage that this enables a larger angle (for example about 3) to be formed between a tangent to the groove and a tangent to the path of the cutter member at the point of intersection.

The pattern of recessed formations is not restricted to such channels in circular or spiral formations. It is possible to employ straight channels arranged in a parallel array as shown diagrammatically at 12c in FIG. 4d or in a radial array. Indeed formations other than channels can be used. For example, the recessed portions may be formed as part-spherical or pyramidal indentations as shown at 12d in FIG. 5. Preferably, the pattern of recessed portions is so arranged and dimensioned that each aperture intersects a plurality of such recessed portions, e.g., channels or indentations. The recessed portions are effective even if randomly disposed with regard to the apertures, and indeed may be truly random instead of a regular array.

A particular advantage arises as a result of the undulating form of the periphery of the apertures in the running surface due to the intersection of the recessed pattern by these apertures. When a hair projecting through an aperture in the guard member is contacted by the blade element it is usually moved by the latter to the portion of the periphery of the aperture which is traversed last by the blade element as it sweeps across the guard member before any substantial cutting of the hair occurs. This tends to reduce the closeness of the shave obtained. However, with a guard member formed from a foil according to the invention such hairs tend to become trapped at the periphery of the aperture concerned due to the undulating form of the periphery of the aperture and are thus severed as soon as they reach the periphery.

Although the blade element is effectively spaced from some parts of the edges of the apertures at which cutting occurs, the spacing (0.0001" to 0.0002") is substantially less than the average thickness of the hairs to be cut (typically 0.006 inch) so that the cut is readily made at any part of the edge.

One of the problems associated with the design of dry shavers is that of achieving a close shave efiiciently, i.e., without causing the shaving head to become hot due to friction between the guard member and the blade element. It will now be apparent that a light but constant contact must be established between the guard member and the blade elements, this usually being achieved by applying some pressure to the cutter member, for example by spring means, to urge the cutter member towards the guard member. Such heating of the cutting head due to the frictional contact between the guard member and blade elements can become excessive and the temperature of the guard member may become sufficiently high to produce considerable discomfort.

The production of heat in this manner also repre sents a waste of energy derived from the power supply for the driving motor of the dry shaver. Whilst this may not be of great importance where mains operated shavers are concerned it is particularly troublesome in the case of battery operated shavers since it gives rise to a larger current drain from the battery than would otherwise be the case so that the useful life of the battery is reduced.

A reduction in the contact pressure between the guard member and blade elements can contribute towards a reduction of such frictional heating but reduction of this pressure below a certain value results in loss of cutting efficiency since the guard member and blade elements are no longer kept in Slll'l'lClCllt contact when the contact pressure is too low.

Thus it is preferred that the area of the running surface which is actually contacted by the blade elements is equal to not more than one-third of the overall area of the running surface of the foil, that is to say the running surface has an overall area of which at least two-thirds is occupied by said recessed portions.

In this way the contact area of the guard member, i.e., that which comes into actual contact with the blade elements, is effectively reduced, so that frictional losses are reduced.

In addition to the above mentioned advantages the provision of the recessed pattern has a further advantage. The recesses tend to accumulate small quantities of finely divided residues of hair and skin together with oils and greases from the skin, and this accumulated material greatly assists the reduction of friction by acting as a lubricant.

Foil for such a guard member may be made by conventional etching processes. Thus one side of the foil may be completely covered by a masking layer and the other side, which is to be the running surface, may be covered by a masking layer formed as a negative of the recessed pattern of channels or indentations which are required to be etched so as to expose the pattern to be etched. The 'foil may then be etched until the channels or indentations have been formed to the required depth, whereupon the running surface may be completely masked and the other surface may be masked by an apertured masking layer. Further etching is continued so as to form apertures extending completely through the foil corresponding to the apertures in the masking layer. The actual disposition of the apertures in relation to the channels or indentations is of no significance provided that the spacing of the channels or indentations is such that the boundary of each apertures has a plurality of intersections with such channels or indentations.

The use of etching in the formation of the apertures and pattern is particularly advantageous where noncircular apertures are required. It is contemplated that a particularly advantageous shape for the apertures would be that formed by the overlapping or intersection of two or more circles, for example trefoil shape, so that the periphery of the aperture as viewed in plan is in effect serrated.

Although the formation of the foils by etching is particularly convenient other methods may be employed. For example, the recessed pattern may be produced by deforming the foil by passing it between a pair of rollers, of which the roller which is in contact with the running surface of the foil is corrugated so as to produce a series of troughs or channels in that surface. Alternatively, such roller may be formed with an array of domed or other projections of a height less than the thickness of the foil so as to produce a pattern of indentations in the foil. It will also be possible for the recessed pattern to be formed by pressing or stamping. The apertures also may be formed mechanically instead of by etching, for example, by piercing.

I claim:

1. In a dry shaver cutting head comprising a guard member having an outer skin engaging face, an inner running face and a plurality of apertures extending through the guard member between said outer face and said running face so that each aperture has a respective orifice in the outer face and a respective orifice in the running face, and a cutter member in engagement with said running face of said guard member for movement relative thereto; the improvement in which said guard member comprises:

(a) a plurality of recessed portions provided in said running face and defining therebetween a running face contact portion with which said cutter member is in contact,

(b) the thickness of said guard member between said recessed portions and said outer face being smaller than the thickness of the guard member between said contact portion and the outer face, and

(c) the orifice of each of said apertures in said running face being constituted partly by said contact portion and partly by at least one of said recessed portions, whereby the periphery of said orifice is of an undulating configuration relative to said runing face.

2. A foil according to claim 1 wherein said recessed portions comprise channels.

3. A foil according to claim 2 wherein said channels comprise adjacent convolutions of a spiral groove.

4. A foil according to claim 2 wherein said channels comprise adjacent convolutions of a plurality of grooves arranged in a multistart spiral.

5. A foil according to claim 2 wherein said channels comprise concentric circular grooves. 1

6. A foil according to claim 2' wherein said channels comprise straight grooves.

7. A foil according to claim 1 wherein said recessed portions comprise discrete indentations.

8. A foil according to claim 1 wherein said running surface has an overall area of which at least two-thirds is occupied by said recessed portions.

References Cited UNITED STATES PATENTS 2,297,915 10/ 1942 Rand et al. 3034.2 2,273,739 2/1942 Te Bas 30-34651 X 2,337,623 12/ 1943 Romao 30-34.2 2,345,263 3/1944 Jepson 30-34651 X 2,346,235 4/1944 Romao 30-34651 X 2,701,414 2/1955 Knapp 30-34651 X 2,959,854 11/1960 Wahl 30-34651 X 3,060,572 10/1962 Duncan 30-34641 X 3,068,568 12/1962 Schnapp 30-34651 3,116,551 1/1964 Anton 30-34651 X FOREIGN PATENTS 644,852 7/ 1962 Canada. 1,208,087 9/1959 France. 1,037,319 8/1958 Germany.

845,832 8/ 1960 Great Britain.

JAMES L. JONES, JR., Primary Examiner US. Cl. X.R. 3043.6 

